1. Field of the Invention
The present invention relates to heatsink apparatuses that cool semiconductors that produce heat, such as microprocessing units (hereinafter referred to as MPUs) used in personal computers and the like, and electronic components having heat-generating portions.
2. Description of Related Art
With higher integration of electronic components, such as semiconductors, and higher frequency of operation clocks, electronic devices have recently been generating an increasing amount of heat. An increasingly important issue in view of normal operation of the electric components is how to maintain contact temperatures of the respective electronic components within a range of an operating temperature. High integration and high frequency are so remarkable in MPUs, in particular, that heat dissipation is a critical issue in order to ensure operation stability, operation life, and the like.
A conventional air cooling system that combines a heatsink and a fan, however, is increasingly insufficient in capacity for cooling electronic components generating a large amount of heat. Thus, a high efficient heatsink apparatus having a higher capacity is proposed, in which a working fluid is circulated, as disclosed in Related Art 1, for example.
A general method of cooling heat-generating bodies generating a large amount of heat, such as MPUs and the like, is to absorb heat at a heat receiver and to dissipate the heat to air from a heat dissipater having a wide area. A conventional technology disclosed in Related Art 1 is explained below, with reference to drawings.
FIGS. 29A and 29B illustrate a configuration of a conventional heatsink apparatus and a structure of a heat receiver, respectively. As shown in FIG. 29A, the conventional heatsink apparatus normally includes heat-receiving unit 1 that removes heat from heat-generating body 2; pipeline 20 that transports a working fluid that has received heat at heat-receiving unit 1; pump 13 that moves the working fluid; and heat dissipater 11 that dissipates heat from the working fluid. A general cooling principle is described below. As shown in the drawings, heat generated in heat-generating body 2 is transferred into heat-receiving unit 1, in which heat exchange with the working fluid circulating therein increases a temperature of the working fluid. Then, the working fluid is transported by pump 13 to heat dissipater 11 through pipeline 20, thereby increasing a temperature of heat dissipater 11. Thereafter, air is fed from fan 10 mounted in the heat dissipater to a surface of heated heat dissipater 11, and thereby the heat is exchanged and dissipated into air.
With reduction in a size of electronic components (fine line manufacturing process), a size of heat-generating bodies themselves has recently been reducing. Accordingly, heat density per unit area has steadily been increasing. Cooling performance of a heatsink apparatus is determined based on performance of both a heat receiver and a heat dissipater. Due to the recent trend of increasing heat density, enhancing the performance of the heat receiver is particularly a big issue. For instance, a heatsink apparatus capable of cooling a heat-generating body having an area of 100 mm2 and generating a heat of 100 W, might not be able to cool a heat-generating body having a reduced heat-generating area of 50 mm2, as a result of a thin line manufacturing process of electronic components, since the size reduction doubles the heat density, thus causing insufficiency in heat absorption capacity.
The heat receiver of the working fluid circulation system, as shown in FIG. 29A, employs a structure shown in FIG. 29B. To increase performance, a pipeline is provided, in which the working fluid circulates in a metal having a high thermal conductivity (e.g., copper, aluminum, and the like). Even in this case, however, heat exchange efficiency from the metal to the working fluid inside the heat receiver significantly relies on an area of an internal wall of the pipeline. Thus, merely providing the pipeline inside the heat receiver does not generally achieve sufficient performance due to a limited heat-receiving area. In addition, insufficient performance is expected to be further remarkable in accordance with future downsizing of heat-generating bodies.
In order to fiber enhance the heat absorption performance of the heat receiver, another conventional technology is provided, as shown in FIG. 30. The conventional technology uses a heat pipe hang a cylindrical shape and closed both ends, and being provided therein with a desired working fluid. A heatsink apparatus using the heat pipe includes a heat receiver that contacts with a heat-generating body and a heat dissipater provided with heat-dissipating fins. Heat from the heat-generating body is transferred to a cylinder wall, and then a phase change (vaporization) of the working fluid occurs on an internal wall and thus draws latent heat of vaporization. Then, vapor is transferred at a high velocity in the cylinder and condenses on an internal wall of the heat dissipater. Heat of condensation is transferred to the fins through the internal wall, and eventually dissipated into air. Subsequently, the condensed working fluid is transferred to the original heat generator by a wick provided on a pipe wall to cause a capillary action. Repeating a cycle of the steps above continues cooling. Since the heat transfer involves a change of phase, the structure achieves a high heat absorption performance, compared to the simple coolant circulation system, as shown in FIGS. 29A and 29B.
[Related Art 1] Japanese Patent Laid-open Publication No. H10-213370
As described above, however, more heat tends to be generated, or heat density tends to be increased, in accordance with further performance increase and the like of electronic components, such as semiconductors. The alternative conventional heatsink apparatus that uses the heat pipe, as shown in FIG. 30, can contain only a small amount of working fluid due to a limited inner capacity. Since a heat pipe used for electronic components mainly has a heat transport capacity of several tens of W level per unit, a plurality of heat pipes are commonly provided in parallel, in order to increase a total heat transport capacity. Although the total heat transport capacity can be increased to a certain level by increasing the number of heat pipes, the problem of heat density increase remains as described above. A measure taken for the problem is to provide heat pipes in parallel on a heat-receiving plate having a high thermal conductivity so as to expand heat as much as possible. Even the measure, however, has a limit in the number of practically functioning heat pipes in view of arrangement. There is still a difficulty remaining in both achieving sufficient heat transport capacity and solving the high heat density issue. Id addition, when a relatively thick heat-receiving plate is used to expand more heat to the plurality of heat pipes, a distance is accordingly longer from the center of a heat-generating body to a vaporization surface where the phase change (vaporization) of the working fluid actually occurs. Thereby, thermal resistance between the center and the vaporization surface increases, thus causing a sharp temperature increase during a time from an onset of heating to an onset of an actual phase change (vaporization), and surpassing a guaranteed operation temperature of electronic components.